1. Technical Field
The present invention relates to, for example, a MEMS (Micro Electra Mechanical Systems) device in which a functional element, such as a resonator, a sensor and an actuator, and/or an electronic circuit are integrated on one substrate, and a method of manufacturing such a MEMS device.
2. Related Art
For example, in a MEMS device that includes a resonator with capacitance as a functional element, the resonator is airtightly sealed, in a vacuum state, in a cavity formed in a substrate. Also, even in the case of a functional element that does not require airtight vacuum seal, the functional element is airtightly sealed in a cavity so as to prevent the influences of dust, moisture, and the like.
In order to form a cavity in such a MEMS device, for example, a sacrificial film is formed in a cavity provided with a functional element, the cavity is covered by a polysilicon lid portion in which an opening (release hole) is formed, and then the sacrificial film is removed through release etching. Furthermore, in order to seal the release hole, a sealing portion is formed, through sputtering, on the lid portion using a sealant.
However, as the mechanical strength (e.g., Young's modules) of polysilicon is low, the lid portion formed of polysilicon easily deforms in a process for forming the sealing portion on the lid portion through sputtering. On the other hand, forming a thick polysilicon lid portion improves the strength of the lid portion, but undesirably makes it difficult to form a minute release hole in the lid portion. In addition, it is preferable that the lid portion and the sealing portion have a high mechanical strength in, for example, processes for forming an insulating film on the lid portion and the sealing portion and planarizing the insulating film.
As related art, JP-A-2010-162629 (paragraphs 0009, 0033, 0034 and 0057, FIG. 1) discloses a method of manufacturing a MEMS device in which a cavity that houses a MEMS structural member (functional element) is formed on a substrate. This manufacturing method includes: forming, on a substrate, a MEMS structural member and a covering structure with a hollow surrounding the MEMS structural member, the hollow being open to an outside; and performing surface etching for the MEMS structural member in a gas phase by supplying an etching gas in an area surrounding the MEMS structural member from the outside. Here, a part of a wiring layer of aluminum and the like constitutes a lid member that covers an upper side of the MEMS structural member. This lid member is provided with one or more openings, and release etching is applied. Thereafter, a sealing layer is formed on the lid member.
On the other hand, JP-A-2006-247815 (paragraphs 0009, 0015 and 0036 to 0051, FIG. 1) discloses a MEMS system composed of a semiconductor device and a MEMS device. Wiring is formed on the semiconductor device, and the MEMS device is formed integrally on the semiconductor device. This MEMS system includes a mirror portion with a variable mirror. The mirror portion is supported by a hinge portion provided on the semiconductor device, and light is reflected by an Al reflection layer provided on a surface of a mirror base layer of the mirror portion. In order to provide the hinge portion, a sacrificial layer is formed on the semiconductor device, a polysilicon film is formed in a through-hole of the sacrificial layer and on the sacrificial layer, and patterning is applied. The mirror base layer of Ti and the like and the Al reflection layer are formed on a surface of the hinge portion using a sputtering technique and the like, patterning is applied, and then the sacrificial layer is removed through etching.
JP-A-2010-162629 (paragraphs 0009, 0033, 0034 and 0057, FIG. 1) and JP-A-2006-247815 (paragraphs 0009, 0015 and 0036 to 0051, FIG. 1) are examples of related art.
In JP-A-2010-162629 (paragraphs 0009, 0033, 0034 and 0057, FIG. 1), as a part of the wiring layer of aluminum and the like constitutes the lid member of a single-layer structure, there is a possibility that the mechanical strength of the lid member is not sufficient in a case where the sealing layer is formed on the lid member through sputtering. On the other hand, in JP-A-2006-247815 (paragraphs 0009, 0015 and 0036 to 0051, FIG. 1), as a cavity need not have an airtight-seal structure and etching for the sacrificial layer is performed in the final stage, the mechanical strength of the hinge portion does not become a problem at the time of formation or treatment of the mirror base layer and the Al reflection layer.